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    SubjectRe: [RFC] propagate gfp_t to page table alloc functions
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    On 25 April 2012 07:30, Andrew Morton <akpm@linux-foundation.org> wrote:
    > On Tue, 24 Apr 2012 17:48:29 +1000
    > Nick Piggin <npiggin@gmail.com> wrote:
    >
    >> > Hmm, there are several places to use GFP_NOIO and GFP_NOFS even, GFP_ATOMIC.
    >> > I believe it's not trivial now.
    >>
    >> They're all buggy then. Unfortunately not through any real fault of their own.
    >
    > There are gruesome problems in block/blk-throttle.c (thread "mempool,
    > percpu, blkcg: fix percpu stat allocation and remove stats_lock").  It
    > wants to do an alloc_percpu()->vmalloc() from the IO submission path,
    > under GFP_NOIO.

    Yeah, that sucks. CFQ has something similar.

    Should just allocate it up front when creating a throttled group.
    Allocate and init when it first gets used schemes are usually pretty
    problematic. Is it *really* warranted to do it lazily like this?

    > Changing vmalloc() to take a gfp_t does make lots of sense, although I
    > worry a bit about making vmalloc() easier to use!
    >
    > I do wonder whether the whole scheme of explicitly passing a gfp_t was
    > a mistake and that the allocation context should be part of the task
    > context.  ie: pass the allocation mode via *current.  As a handy
    > side-effect that would probably save quite some code where functions
    > are receiving a gfp_t arg then simply passing it on to the next
    > callee.

    Both paragraphs make a lot of sense. Conceptually. :)
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